Matrix cracking in composite laminates is the first macroscopic damage mode to be readily detected. Polarimetric sensors embedded in composite laminates can detect the development of this damage and they have an advantage over other sensors in being able to sense damage over long gauge lengths (potentially, many metres). In this paper, the sensitivity of a polarimetric sensor manufactured from Hi-Bi PANDA fibre has been measured experimentally and a phase-strain model available in the literature has been used to determine the characteristic parameters of the sensor. The sensitivity of such sensors embedded in unidirectional composites is shown to be in good agreement with theoretical predictions, allowing for material non-uniformity. In the case of cross-ply laminates, which are transversely anisotropic, it is shown that sensor sensitivity is dependent on the relationship of the sensor axes to the composite axes, as well as on the degree of sensor twist. Maximum sensitivity is obtained for a combination of low twist angle and congruence between the sensor optical axes and the composite axes. Twist angles of greater than 90° give rise to sensitivities, which, although lower, are reasonably constant and approximately the same as the sensitivity of the sensor in a unidirectional composite.
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